1. Field of the Invention
This invention relates to optical instruments such as photographic cameras having a pentaprism and, more particularly, to a device for retaining the pentaprism in the adjusted position.
2 . Description of the Prior Art
To fixedly secure a pentaprism to position within an optical instrument, particularly a photographic camera, the following two main requirements must be fulfilled. In this connection, various improvements have been attempted. (1) When the pentaprism is engaged to a support framework therefor, the holding pressure is directed to both the bottom and rear faces of the pentaprism so that the resulting position of the pentaprism is automatically adjusted with high accuracy, since the bottom and rear faces of the pentaprism are usually designed to serve as the reference faces for such adjustment. (2) The mount assembly tends to hold the pentaprism in the adjusted position so that, after accidental displacement of the pentaprism by application of external shock to the camera, the removal of such shock will result in return of the pentaprism to the initial adjusted position.
In the prior art, the holding means is constructed in the solid form so that a rigid member is placed over the pentaprism and fixedly secured to the camera housing by means of screw fasteners. For shock absorbing purposes, a sponge sheet is inserted into a space between the upper surface of the pentaprism and the rigid member. In another method, a presser plate is placed over the pentaprism and connected through springs to the support framework for the pentaprism so that the pentaprism is retained by the force of the springs.
Recently, however, the prime requisites for photographic cameras are light-weight and small size for convenient and handy use. Since the advent of miniaturization in the production of integrated circuits, semiconductor arrays and printed circuit networks, there is an increasing demand of camera control systems of superior performance which the prior art means and methods of providing pentaprism mounting devices make impossible to achieve. In other words, as the weight and bulk of the camera are decreased, the spaces between the pentaprism and the holding means and between the support member for the pentaprism and the camera housing wall are decreased. Accordingly, the use of the sponge sheet as the shock absorbing means and the springs as the position control means which are necessary in the afore-mentioned conventional pentaprism mount assemblies is not compatible with the requirment of achieving minimization of the weight and bulk of the camera. This requirement when combined with the requirement, for electronic conversion of the camera control system, and also as the resulting mechanism of the camera is made more complicated to occupy an increased proportion of the total space available within the camera housing, it is impossible not to make use of the space between the non-functional faces of the pentaprism, that is, the roof faces and the top panel of the camera housing in arranging the electronic circuit components. For this purpose, the pentaprism must be retained in the efficiency accurately adjusted position, while preserving the space which the electronic circuit components are intended to occupy.